Adjustable pressure relief valves are known. Such pressure relief valves are used, for instance, in conjunction with cleaning devices that utilize high pressure water, such as are found in car wash facilities. In certain applications such pressures may be as much as 1500 pounds per square inch. The pressure relief valve is used as a safety device to vent pressure in the event that the pressure exceeds a selected setting. Some pressure relief valves have a fixed pressure above which the valve vents. Other valves have a pressure adjuster for selectively varying the pressure above which the valve vents. A pressure adjuster comprises a component of the pressure relief valve to permit an operator to readily adjust the pressure at which the pressure relief valve opens and vents pressure. The pressure adjuster may set by hand or by use of a turning instrument, such as a wrench or the like.
A known pressure relief valve has a body section with pressure bearing components contained therein. A pressure adjuster is threadedly engaged with the body. A coil spring contained within the adjuster bears on the pressure bearing components contained within the body, urging such components into a sealing engagement with a valve seat. By rotating the pressure adjuster on the threads, the biasing force exerted by the spring upon the pressure bearing components is changed as desired. The pressure of incoming fluid to the valve body exerts pressure on the pressure bearing components that counters the biasing force exerted by the spring.
When the countering force exerted by the incoming fluid pressure exceeds the force exerted by the biasing spring, the spring is further compressed by the pressure bearing components and a venting port is exposed. Fluid pressure then escapes through the vent. When countering force exerted by the inlet fluid pressure again equals the biasing force exerted by the adjusting spring, the spring acts on the pressure bearing components, urging such components into a sealing engagement with a valve seat and thereby closing off the vent. The pressure bearing components define a portion of the fluid retaining boundary that maintains the fluid pressure integrity of the pressure relief valve.
A problem with the conventional device described above is that the pressure bearing components disposed within the body of pressure relief valve are retained therein by action of the biasing force exerted on the components by the adjusting spring. Notwithstanding prominent warnings to the contrary, the pressure adjuster is, on occasion, inadvertently removed while fluid inlet pressure is acting upon the pressure relief valve. Inadvertent removal of the pressure adjuster causes the pressure bearing components disposed within the body to be expelled therefrom at high velocity. This interrupts the fluid retaining boundary that maintains the fluid pressure integrity of the pressure relief valve. Moreover, these components become missiles that could cause injury to an operator. The escaping high pressure fluid poses an additional potential risk of injury to an operator.
Accordingly, it would be a decided advantage in the industry to have an adjustable pressure relief valve wherein the pressure bearing components of the valve are retained within the body of the valve in the event that the pressure adjuster is inadvertently removed while fluid pressure is acting on the pressure relief valve. Such a pressure relief valve would decidedly improve the safety of the working environment in which the valve was installed.